1. Field
The presently disclosed subject matter relates to an optical deflector including sense elements (piezoelectric sensors).
2. Description of the Related Art
A prior art two-dimensional optical deflector is constructed by a mirror, a movable frame surrounding the mirror for supporting the mirror, a pair of meander-type inner piezoelectric actuators fixed between the movable frame and the mirror and serving as cantilevers for rocking the mirror with respect to an X-axis of the mirror, a support body surrounding the movable frame, and a pair of meander-type outer piezoelectric actuators fixed between the support body and the movable frame and serving as cantilevers for rocking the mirror through the movable frame with respect to a Y-axis of the mirror perpendicular to the X-axis (see: U.S. Patent Application Publication No. 2011/0292479A1 & JP2010-122480A).
Generally, in an optical scanner, the mirror is rocked with respect to the X-axis for a horizontal deflection at a high frequency, while the mirror is rocked with respect to the Y-axis for a vertical deflection at a low frequency.
In the described prior art two-dimensional optical deflector, each of the piezoelectric actuators includes a drive element and a monitor (sense) element separated from each other by a separation groove. Therefore, when the piezoelectric actuators are driven by their drive elements, the flexing amounts of the piezoelectric actuators are sensed by their sense elements. As a result, the actual flexing amounts of the piezoelectric actuators are controlled by the feedback of the output signals of the sense elements in such a way that the amplitudes of the output signals of the sense elements are brought close to predetermined values. Thus, the deflection of the optical deflector can be controlled with high accuracy.
In the above-described prior art two-dimensional optical deflector, however, since the sense elements are provided in the entire piezoelectric actuators, the provision area of the drive elements in the piezoelectric actuators is decreased so that the rocking forces of the piezoelectric actuators are weakened, thus decreasing the deflection angles of the optical deflector. Also, since long wiring lines are required to be connected to the drive elements and the sense elements, the resistance of the wiring lines is increased. Further, since the two-dimensional optical deflector is conventionally manufactured by the micro electro mechanical system (MEMS) technology, the two-dimensional optical deflector is so fined so that the width of the drive elements and the width of the sense elements are very small, i.e., several hundreds of μm, and also, the spacing between the drive elements and the sense elements is very small. Therefore, the high frequency sense signals from the sense elements cannot be detected due to their crosstalk. As a result, it is impossible to accurately control the actual flexing amounts of the piezoelectric actuators by the feedback of the output signals of the sense elements.